Modular potentiometer

ABSTRACT

A potentiometer module, containing circular resistance and collector paths with a sliding control bridging between the paths, is combined with other similar modules in side by side, stacked relation to form one of a possible assortment of multiple potentiometer controls. The modules are fastened together by four stack bolts extending through them and screwed at one end into a face plate formed on the back of a threaded bushing. The face plate and bushing are at one end of the stacked modules, and a shaft inserted through the bushing controls all modules simultaneously. Several alternative arrangements of the modules are shown, and in one, for example, two concentric shafts each control selected modules. Each potentiometer module has a rectangular case containing a rotor with a movable contact. A collector ring is disposed axially to one side of the movable contact and a resistance track deposited on a base is disposed to the other side of the movable contact. The rotor passes completely through the module and has an opening through it to allow passage of shafts connected to other modules.

I United States Patent 1 2 Slagg et a]. [4 1 July 11, 1972 [54] MODULARPOTENTIOMETER 2,706,760 4/1955 Mucher ..338/174 X [72] Inventors: JamesE. Slagg, South Milwaukee; Grant get W. Nelson, Milwaukee; Jerry T.Mofiitt, 2431749 12/1947 G 132 x Cudahy; Joseph A. Baum, wauwatosa, arant of 2,758,182 8/1956 Mucher ..338/131 [73] Assignee: Allen-BradleyCompany Primary Examiner-Lewis l-l. Myers Assistant Examiner-D. A. Tone[22] Ffled' April 1971 Attorney-Barry E. Sammons and Arthur H. Seidel[21] App1.No.: 132,463

[57] ABSTRACT [52] US. Cl ..338/132, 338/128, 338/ l34, A potentiometermodule, containing circular resistance and 174 collector paths with asliding control bridging between the [5 l Int. Cl ..H0lc 9/02 paths iscombined with other similar modules in side by side,

of Search l 34, tacked relation to fo -n1 one of a assortment of multi-333/129 130, 133 ple potentiometer controls. The modules are fastenedtogether by four stack bolts extending through them and [56] ReferencesCited screwed at one end into a face plate formed on the back of athreaded bushing. The face plate and bushing are at one end UNITEDSTATES PATENTS of the stacked modules, and a shaft inserted through thebush- 1,466,293 8/1923 Brooks ..338/132 ing controls all modulessimultaneously. Several alternative 1,613,606 1 1 927 Flammer ...338/132arrangements of the modules are shown, and in one, for exam- 2,059,712 11/ 1936 Schellenger ...200/153 ple, two concentric shafts each controlselected modules. 2,720,572 10/ 1955 Moore ..338/90 Each potentiometermodule has a rectangular case containing 2,676,226 4/ l 954 Mucher l 3 la rotor with a movable contact; A collector ring is disposed ax-2,125,954 8/ 1938 Richt -m l 32 ially to one side of the movable contactand a resistance track 2,852,644 5 Elliott 338/174 deposited on a baseis disposed to the other side of the mova- |,415,534 1922 Donle blecontact. The rotor passes completely through the module Arisman et aland has an opening through it to allow passage of hafts con. 3,01 l Mairnected to other modules 2,863,972 12/1958 Barton 2,257,979 10/ 1 941Rubinstein ..64/4 24 Claims, 9 Drawing Figures Patented July 11, 1972 5Sheets-Sheet l INVE NTORS JAMES E. SLAGG GRANT W- NELSON JERRY T.MOF'FITT JOSEPH A. BA LINT ATTRNEY Patented July 11, 1972 5 Sheets-Sheet2 INVENTORS JAMES E. SLAGG GRANT W. NELSON ATTORNEY Patented July 11,1972 5 Sheets-Sheet s INVE NTORS JAMES E. SLAGG GRANT W. NELSON JERRY T-MOFFlTT JOSEPH A.BAL|NT ATTORNEY Patented July 11, 1972 3,676,822

5 Sheets-Sheet 4 INVENTORS JAMES E. SLAGG GRANT W. NELSON JERRY T.MOFFITT JOSEPH .BALINT ATTORNEY Patented July 11, 1972 5 Sheets-Sheet 5INVENTORS JAMES E.SLAGG GRANT W.NELSON JERRY T. MOFFITT JOSEPH A.BALlNTc ATTORNEY MODULAR POTENTIOMETER BACKGROUND OF THE INVENTION The presentinvention relates to variable resistors, or potentiometers, having acircular resistance track and a shaft which rotates a conductive brusharound the resistance track to vary the resistance between the brush andthe ends of the track.

Typically, the shaft is inserted through a bushing which is adapted forattachment to a control panel or other mounting surface. A case attachedto the back of the bushing contains a circular resistance track disposedaround and concentric with the axis of the shaft. A conductive collectoris also disposed around the axis of the shaft and in the same plane asthe resistance track. A conductive brush connected to the end of theshaft bridges the gap between the resistance track and collector andmoves around the track when the shaft is rotated. As in the patent toDehn et al., US. Pat. No. 2,868,931 titled Variable Resistance Control,"the collector may be annular shaped, having a hole through its centerthrough which the shaft may pass.

By extending the shaft through the collector and back surface of thecase, other specially adapted cases also containing resistance andcollector elements can be coupled to the back of the first potentiometersection. The shaft extends through the first potentiometer section tocontrol the second potentiometer section.

Prior potentiometers are very inflexible. The first potentiometersection is an integral part of the shaft and bushing and subsequentpotentiometer sections must be specially adapted to attach to its back.Multiple section potentiometers are generally assembled in the factoryand require the customer to order and stock each type of control heneeds. The variety of control types needed by a customer can be quitelarge, including not only a variety of special physical configurationssuch as vernier controls and concentric shaft arrangements withdiffering numbers of potentiometer sections and shaft shapes, but also awide range of electrical values for each potentiometer section.

Another limitation on present controls is their depth, or axial length.With multiple section potentiometers the maintenance of proper alignmentbetween the rotors of each section becomes more difficult as the numberof sections is increased. Misalignment causes excess wear on thecoupling mechanism between sections and makes fine adjustment of theresistance setting of the control difficult. As more potentiometersections are combined one on back of the other, the increased leverageand the inadequate means presently used to attach them together add tothe likelihood of misalignment. Typically, the potentiometer section tobe attached has a series of tabs protruding from its front surface whichtabs snap around the case of the potentiometer section to which it isattached. Particularly when more than two sections are combined, thecontrol becomes very susceptible to damage from bumping and consequentmisalignment during assembly of the equipment.

Another problem encountered when combining potentiometer sections, isthe necessary increase in their diameter required to accommodate theshaft passing completely through potentiometer sections. The diameter ofthe annular shaped collector in prior devices is increased to allow forthe shaft opening through it, and consequently the diameter of thesurrounding resistance track must be relatively large to providesufficient insulation between the concentric resistance track andcollector. As a result, combining potentiometer sections into singlecontrols has resulted in either an increase in their size or cost ofmanufacture.

SUMMARY OF THE INVENTION The present invention comprises a potentiometermodule connectable to a bushing and shaft and connectable to othersimilar potentiometer modules to form a multiple section control. Themodules are securely fastened together by a plurality of stack boltsinserted through them and into the bushing. The

potentiometer module includes a case having a rotor carrying a movablecontact, a resistance track axially disposed to one side of the movablecontact and in electrical contact with the movable contact, and acollector axially disposed to the other side of the movable contact andin electrical contact therewith. The rotor communicates with both thefront and back surface of the potentiometer module for coupling to ashaft or other potentiometer module.

A general object of the invention is to provide a universalpotentiometer module which can be combined with other modules to form amultiple section control. The module can be connected directly tothebushing or mounted on the back surface of another module.

Another object of the invention is to provide a potentiometer modulewhich can be securely fastened to other modules. The modules arestructurally similar and have stack bolt openings passing completelythrough them from front to back. When combined to form a control,therefore, the openings are aligned to receive stack bolts which passcompletely through the modules and securely fasten them to the bushing.Assembly is easy and rotor alignment is maintained regardless of thenumber of potentiometer modules used.

Another object of the invention is to provide a potentiometer modulewhich is a universal building block for customerbuilt controls. Modulesof difiering resistance value and taper can be stocked by customersalong with bushings, shafts, stack bolts, switches and other functionalmodules. Any number and order of modules can be combined to provide thedesired control. The hardware used is essentially identical for eachcontrol with the exception of the stack bolt length. Thus maximumflexibility is obtained with a minimum available stock.

Still another object of the invention is to provide a potentiometermodule having a rotor which extends completely through the module, butdoes not necessitate an increase in case size. By removing the collectorfrom the plane of the resistance track to a plane on the opposite sideof the movable contact, a relatively large opening can be provided forthe rotor without increasing the outside diameter of the resistancetrack. The movable contact is thus disposed axially between theresistance track and the collector. The contact pressure necessary tomaintain electrical connection is obtained by biasing the movablecontact against both the resistance track and the collector. The forcesthus generated are substantially equal and opposite so that no momentsare applied to the rotor.

The foregoing and other objects and advantages of the invention willappear from the following description. In the description reference ismade to the accompanying drawings which form a part hereof, and in whichthere is shown by way of illustration and not of limitation a preferredembodiment of the invention. Such embodiment does not represent the fullscope of the invention. But rather the invention may be employed in manydifferent embodiments, and reference is made to the claims herein forinterpreting the breadth of the inventron.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded isometric viewof a dual section control incorporating the potentiometer module of thepresent invention,

FIG. 2 is a view in elevation of the control in FIG. 1 with the firstpotentiometer module in cross section taken along the shaft axis andwith parts of the second potentiometer module cut away,

FIG. 3 is an exploded isometric view of a potentiometer module,

FIG. 4 is a plan view of the base which forms a part of thepotentiometer module,

FIG. 5 is a front plan view of the potentiometer module,

FIG. 6 is a view in elevation of a single section concentric shaftcontrol with switch,

FIG. 7 is an exploded isometric view of a single section concentricshaft vernier control,

FIG. 8 is a view in cross section of a reduction gear module which formspart of the control shown in FIG. 7, and

FIG. 9 is a view in cross section with parts in the round taken alongthe shaft axis of a dual section concentric shaft control incorporatingthe potentiometer module of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, acylindrical bushing l threaded along its outside surface includes asquare face plate 2 formed at its back end perpendicular to the centralaxis of the bushing 1. The bushing 1 also includes a circular mountingsurface 3 which extends forward from the front surface of the face plate2, completely around the bushing 1. The bushing 1 is typically insertedthrough a hole in a control panel (not shown in the drawings) and themounting surface 3 is drawn tightly against the back surface of thecontrol panel by tightening a nut around the bushing 1 (not shown)against the front surface of the control panel. Four threaded stack boltholes 4 are formed through the face plate 2, each located near one ofits comers. A circular recess 5 is formed in the back surface of theface plate 2 concentric with a shaft opening 6 which extends completelythrough the bushing 1, along and concentric with its central axis.

A square locating plate 7 having a large central opening is mountedagainst the back surface of the face plate 2. The locating plate 7 alsohas four stack bolt holes 8, one located near each corner and inalignment with the stack bolt holes 4 in the face plate 2. A locatinglug 9 is formed midway along one edge of the locating plate 7. Thelocating lug 9 extends axially forward, past the face plate 2 and midwayalong the length of the bushing 1. When mounted on a control panel, thelocating lug 9 is inserted through a hole or slot in the panel toproperly orient the control and prevent it from rotating.

A shaft 10 with a molded plastic female coupler 11 connected to its backend, extends forward through the shaft opening 6. The outer rim of thefemale coupler 11 has a diameter larger than that of the shaft opening6, and its forward edge seats in the recess 5 formed in the back of theface plate 2. The female coupler 11 is annular shaped having a centralopening into which a base key 13 and two wing keys 14 extend radially.The wing keys 14 are spaced slightly apart and located directly oppositethe base key 13 on the inside surface of the coupler 11. A portion ofthe female coupler 11 clears the rear surface of the face plate 2 and alimit tab 12 is formed on the outer rim of this portion. The limit tab12 extends radially outward and is free to revolve with the shaft 10.

Fastened to the back side of the locating plate 7 is a firstpotentiometer module 15. Referring to FIG. 3, the module 15 includesthree basic components, a rectangular shaped case 16, a rotor 17 and abase 18. A front plan view of the base 18 is shown in FIG. 4 and a frontplan view of the module 15 is shown in FIG. 5. The case 16 is formedfrom molded plastic or metal and has a square cross section with sidesaligned with the sides of the face plate 2 and locating plate 7. Fourstack bolt holes 19 pass completely through the case 16 from front toback, and align with the stack bolt holes 8 in the locating plate 7. Ashaft opening 20 is formed through the center of the case 16 from frontto back, and a deep circular recess is formed in the back surface of thecase 16 to form a compartment 21. The diameter of the compartment 21 isless than the width of the case 16 and rectangular slots are cut in thetop and bottom sides of the case 16 through to the compartment 21. Ashallow circular recess 22 is formed on the front surface of the case16, concentric with the shaft opening 20. As shown best in FIGS. 2 and5, an annular-shaped wall 22 is thus formed and separates the frontrecess 22 from the compartment 21. When assembled, the coupler 11including the limit tab 12, fits into the front recess 22 against thewall 22'. A stop is formed and extends upward from the bottom of thefront recess 22 and forward from the wall 22 to prevent completerotation of the shaft 10 by engagement with the limit tab 12.

nun

As shown in FIGS. 2 and 3, a metallic collector ring 23 is located inthe compartment 21 attached to the back side of the wall 22'. Thecollector ring is annular shaped, having an outside diameter less thanthat of the compartment 21 and an inside diameter larger than the shaftopening 20. A collector terminal 24 extends from the collector ring 23downward through the bottom side of the case 16.

As shown in FIGS. 2 and 3, the rotor 17 includes a hollow sleeve 26 ofmolded plastic which fits snugly in the case shaft opening 20. Both endsof the sleeve 26 are identical. The front end of the sleeve 26 fitssnugly into the female coupler 11. As shown in FIG. 5, it has a narrownotch which forms a base keyway 32 and a wider notch directly oppositewhich forms a wing keyway 33. The keyways 32 and 33 receive the keys l3and 14 of the female coupler 11. A plastic flange 27 is formed midwaybetween the sleeve ends and partway around its circumference. A movablecontact assembly 28 is firmly attached to the front face of the flange27 by sonic welding a pair of plastic rivets 27. The movable contactassembly 28 includes a metallic wiper ring 29 which completely encirclesthe sleeve 26 and is deformed to bend axially backward. A conductivebutton 30 is attached to the wiper ring 29 at a point directly oppositeits attachment to the flange 27. Also included is a contact ring 31attached to the front face of the wiper ring 29 at the flange 27. Itwraps substantially around the sleeve 26 and has two contact ends whichare deformed to bend axially forward. This deformation creates a springforce acting to press the contact ends of the wiper ring 29 against thecollector ring 23 when the sleeve 26 is inserted into the shaft opening20.

As shown in FIGS. 2-4, the module base 18 is formed of molded plasticand has an annular-shaped body 34 which fits within the compartment 21of the case 16. A recess 35 is formed in the back surface of the body 34concentric to its central opening. A rectangular cap 36 is formed on thetop edge of the body 34, and a rectangular pedestal 37 is formed on itslower edge directly opposite the cap 36. The cap 36 and pedestal 37tightly engage the case 16 and provide means of anchoring electricalterminals connected to a resistance track 38 deposited in the frontsurface of the body 34. The track 38 comprises a layer of conductingmaterial in the form of metals and metal oxides dispersed within a glassmatrix. The track 38 extends around the front surface and terminatesabove the pedestal 37. Each of the two ends of the resistance track 38are electrically and mechanically connected to one of the two terminals39. The terminals 39 extend through the pedestal 37 out the bottom sideof the module 15.

When assembled, the rotor 17 is inserted first into the case compartment21 followed by the base 18 which is retained by hot staking portions ofthe plastic case 16 against the back surface of the base 18. A housingcontaining the collector 23, rotor 17 and resistance track 38 is thusformed. The front end of the sleeve 26 protrudes through the shaftopening 20 and is substantially flush with the front surface of themodule 15. The back end of the rotor sleeve 26 protrudes through theopening in the base 18 and is substantially flush with the back surfaceof the module 15. The length of the rotor sleeve 26 is not crucial tothe inventionit is necessary only that the rotor 17 communicate withboth the front and back surface of the module 15 in order that it may becoupled to adjacent modules, stacked either in front or back of themodule 15. The movable contact 28 is located axially between theresistance track 38 and the collector ring 23. The permanent deformationof the wiper ring 29 spring biases the button 30 against the resistancetrack 38 insuring good electrical contact. Likewise, the permanentdeformation of the contact spring 31 spring biases its contact endsagainst the collector ring 23. The button 30 of the wiper ring 29 iscircumferentially aligned between the contact ends of the contact spring31. The moments generated by the contact bias forces are equal andopposite and therefore generate no net moment, or transverse torque onthe rotor 17.

All of the potentiometer modules referred to subsequently herein arestructurally similar to the module described above. To more clearlydescribe the various controls which can be built with the potentiometermodule of the present invention, however, the modules are givendifferent reference numbers. For example, in the dual section controlshown in FIGS. 1 and 2, a second potentiometer module 40 is fastened tothe back surface of the first module 15. A link 41 having identicalfemale coupling connections at each end is disposed between the modules15 and 40 to connect their rotors 17. The link 41 fits snugly in therecess on the back surface of the first module 15 and in the recess 22formed on the front surface of the second module 40.

A square back plate 42 covers the back surface of the second module 40,and four stack bolt holes 43, each located near one corner, are formedin the back plate 42. Four stack bolts 44 having threaded ends areinserted through the back plate 42, the second module 40, the firstmodule 15, the locating plate 7, and into the face plate 2. The surfaceof the back plate 42 is recessed adjacent each of its comers tocountersink the stack bolt heads. By using stack bolts 44 of appropriatelength, the second potentiometer module can be removed to form a singlesection control, or other modules can beadded. Regardless of the numberof potentiometer modules, the stack bolts 44 can be tightened to form arigid structure virtually impervious to forces tending to misalign themodules. Threaded stack bolts 44 are shown herein and provide for easydisassembly of the control, however, metal or plastic rivets can also beused when cost reduction is a more important factor and as used herein,the term stack bolt is intended to include rivets and other similarfastening devices which are inserted through openings in parts to clampthem together.

The potentiometer module is a building block which can be used to formnumerous types of controls. For example, as shown in FIG. 9, a doublesection, concentric shaft control is formed with a first potentiometermodule 45 and a second potentiometer module 46. The bushing 1, faceplate 2, and back plate 42 are identical to those in the double sectioncontrol described above. The shaft, however, is divided into an outershaft 47 and a concentric inner shaft 48. Attached to the back end ofthe outer shaft 47 is a female coupler 49, identical to the coupler 11described above. The outer shaft 47 engages and drives the rotor 17 ofthe first potentiometer module 45. The inner shaft 48, on the otherhand, extends through the outer shaft 47, its coupler 49, and the firstpotentiometer module 45. A female coupler 50 is formed on the back endof the inner shaft 48 to engage and drive the rotor 17 of the secondpotentiometer 46. Because the sections of the control are drivenseparately, a square spacer 51 having four aligned stack bolt holes (notshown in the drawing) is inserted between the first and second modules45 and 46 to separate their rotors and provide space for the femalecoupler 50. Four stack bolts 52 are inserted through the back plate 42,the second module 46, the spacer 51, the first module 45, the locatingplate 7 and into the face plate 2. Because of the added spacer 51, thestack bolts 52 are slightly longer than those used with the conventionaldouble section control described above. Of course, additional modulescan be added to the con trol and driven by either the outer shaft 47 orinner shaft 48. For example, additional potentiometer modules can bestacked directly behind the first module 45 with links 41 used to coupletheir rotors 17. Alternatively or additionally, potentiometer modulescan be stacked behind and coupled to the rotor 17 of the second module46.

As shown in FIG. 6, the concentric shaft arrangement is also useful toseparately drive a first potentiometer module 53 and a switch 54. Theswitch section 54 can be either rotary or push-pull, the only constrainton its design being the placement of four stack bolt holes in alignmentwith the holes in the potentiometer module 53. A spacer 51 is insertedbetween the module 53 and the switch module 54 although it may also beformed as an integral part of the switch module 54. The outer shaft 47drives the rotor 17 of the potentiometer module 53 as in the concentricshaft arrangement described above, and the inner shaft 48 is attached tothe switch section 54 by a suitable coupling means (not shown in thedrawing). Additional modules can be added and driven by either shaft 47or shaft 48.

As shown in FIGS. 7 and 8, the potentiometer modules can also be used toform a vernier control. A potentiometer module 55 and a reduction gearmodule 56 are combined with a bushing 1, face plate 2, locating plate 7,and back plate 42 identical to those described above. The reduction gearmodule 56 has a square cross section and contains four stack bolt holes62 aligned with the stack bolt holes in the face plate 2 and locatingplate 7. The reduction gear module 56 is attached to the back surface ofthe locating plate 7 and is driven by an outer shaft 57 which extendsthrough the bushing 1, faceplate 2, locating plate 7 'and a centralopening in a front cover 59 of the module 56. A first sun gear 58 isattached to the back end of the outer shaft 57 and a circular retainerflange 60 is formed around the outer shaft 57 immediately forward of thesun gear 58 to retain the shaft 57 to the front cover 59.

As shown in FIG. 8, located within the reduction gear module 56 is agear train connecting the sun gear 58 to a female coupler 61, rotatablyattached to the back surface of the module 56. The interior of themodule 56 is circular in cross section and has a gear rack 71 around itsentire circumference. The first sun gear 58 engages and drives a pair offirst planet gears 72 which engage and revolve around the gear rack 71when the outer shaft 57 is rotated. The first planet gears 72 are eachrotatably attached to the front surface of a circular flange 73 on asecond sun gear 74. The second sun gear 74 engages and drives a pair ofsecond planet gears 75 which engage and revolve around the gear rack 71.The second planet gears 75 are each rotatably attached to the frontsurface of a flange 76 which is formed as an integral part of a driveshaft 77. The drive shaft 77 extends out through an opening in the backsurface of the reduction gear module 56 and attaches to a circularpedestal 63, upon the back surface of which the female coupler 61 isintegrally formed. Thus the gear train links the outer shaft 57 to thefemale coupler 61 to drive the latter at a substantially reduced rate ofrotation.

The sun gears 58 and 74 and the drive shaft 77 each have centralopenings through them to accommodate an inner, concentric shaft 66 whichextends completely through the outer shaft 57, the reduction gear module56, and the potentiometer module 55.

In the preferred embodiment the female coupler 61 and the circularpedestal 63 extend out the back surface of the reduction gear module 56,and as a consequence, a square spacer 64 having a large central openingto accommodate the pedestal 63 is inserted between the reduction gearmodule 56 and the potentiometer module 55. The female coupler 61directly engages and drives the front end of the rotor 17 in thepotentiometer module 55. The spacer 64 need not be a separate item, butinstead may be formed as an integral part of the gear reduction module56.

Formed on the back end of the inner shaft 66 is a plastic coupler 67having two wing keys 68 and a base key 69. The coupler 67 mates with anddrives the back end of the rotor 17 in the potentiometer module 55. Aback plate 42 covers the back surface of the module 55 and four stackbolts 70 tightly fasten the components of the vernier control to theface plate 2.

By rotating the inner shaft 66, the rotor 17 of the potentiometer module55 is controlled directly, whereas rotation of the outer shaft 57controls the rotor 17 at a substantially reduced rate through the gearreduction module 56. Other potentiometer modules can be added andcontrolled in like fashion by inserting them between the spacer 64 andthe potentiometer module 55 and coupling their rotors 17 together withlinks 41. Also, more concentric shafts can be added and coupled toselected potentiometer modules.

It is apparent that by using identical potentiometer modules with aminimal amount of hardware, a large number of different controls can bebuilt. Because parts are kept to a shaft even when large numbers ofmodules are combined and subjected to external bending forces. Finally,displacing the collector ring axially to the side of the movable contactopposite the resistance track allows passage of two or more concentricrotatable members through the center opening in a resistance track ofminimal outside diameter and substantially reduces the moment forces onthe rotors, which forces make fine control settings difficult and causeexcessive wear of the couplers between modules.

We claim:

1. A potentiometer module the combination comprising:

a case having a front and back surface;

a rotor connected to said case to rotate about an axis, said rotorhaving a movable contact;

a collector connected to said case and disposed axially to one side ofsaid movable contact and in electrical contact therewith; and

a resistance track connected to said case and disposed axially to theother side of said movable contact and in electrical contact therewith;

wherein said rotor includes a sleeve having ends which communicate withthe front and back surfaces of said case and said collector andresistance track are disposed around said sleeve.

2. A potentiometer module as recited in claim 1, wherein said sleeve hasidentical coupling means at its ends.

3. The potentiometer module as recited in claim 1, wherein said movablecontact comprises:

a wiper which is spring biased against said resistance track by a forceacting axially in one direction; and

a contact ring which is spring biased against said collector by a forceacting axially in the opposite direction.

4. The potentiometer module as recited in claim I, wherein saidresistance track is formed on an annular-shaped base disposed aroundsaid rotor sleeve and connected to said case.

5. A control the combination comprising:

a bushing adapted to attach to a control panel;

a shaft extending through said bushing;

a coupler connected to the back end ofsaid shaft;

a first potentiometer module having front and back surfaces, said firstmodule including a rotor which communicates with the front surface ofsaid first module to connect with said coupler and which extends throughsaid first module to communicate with its back surface;

a second potentiometer module having front and back surfaces, saidsecond module including a rotor which communicates with the frontsurface of said second module to connect with the rotor of said firstmodule and which extends through said second module to communicate withits back surface; and

a plurality of stack bolts each passing completely through said firstand second modules to fasten them to the bushing.

6. A control as recited in claim 5, wherein said first and secondpotentiometer modules are structurally identical, each rotor having asleeve which communicates with the front and back surfaces of the moduleand a movable contact, each module also having a collector disposedaround said rotor sleeve and axially to one side of said movable contactto make electrical contact therewith and a resistance track disposedaround said rotor sleeve and axially to the other side of said movablecontact to make electrical contact therewith.

7. A control the combination comprising: a bushing adapted to attach toa control panel and having a shaft opening extending through it fromfront to back; a face plate disposed around the opening at the back endof the bushing and perpendicular to the central axis of the shaftopening;

a first potentiometer module fastened to the face plate, said firstmodule having a rotor in alignment with the shaft opening axis, whichrotor extends completely through the first module and has a centralconcentric opening completely through it;

an outer shaft rotatably retained within said shaft opening andconnected to the rotor of said first module, said shaft having a centralconcentric opening;

a second potentiometer module structurally identical to the firstpotentiometer module and connected to the first potentiometer module,said second module having a rotor aligned with the rotor of said firstpotentiometer module; and

an inner shaft rotatably retained within and passing through theopenings in the outer shaft and the rotor of the first module to connectwith the rotor of the second module.

8. The control as recited in claim 7 wherein a plurality of stack boltsextend through aligned openings in the first and second potentiometermodules to connect said modules to the face plate, wherein said alignedopenings are substantially parallel to the axis of rotation of saidrotors.

9. The control as recited in claim 8 wherein the module rotors eachinclude a movable contact connected to a sleeve and each module includesa collector disposed around said sleeve and axially to one side of saidmovable contact and -a resistance track disposed around said sleeve andaxially to the other side of said movable contact.

10. A control the combination comprising:

a bushing adapted to attach to a control panel or the like and having ashaft opening extending through it from front to back;

a face plate disposed around the opening at the back end of the bushingand perpendicular to the central axis of the shaft opening;

a gear reduction module fastened to the face plate, said gear reductionmodule including a gear train with an output which rotates at a reducedrate of rotation with respect to a rotatable input;

an outer shaft rotatably retained within said shaft opening andconnected to rotate said gear train input, said outer shaft having acentral concentric opening;

a first potentiometer module fastened to said gear reduction module,said first module having a rotor in alignment with the shaft openingaxis and coupled to said gear train output, which rotor extendscompletely through the first potentiometer module and has a centralconcentric opening completely through it; and

an inner shaft rotatably retained within and passing through the outershaft and reduction gear module to connect with the rotor of the firstpotentiometer module.

11. The control as recited in claim 10, wherein a plurality of stackbolts extend through aligned openings in the gear reduction module andfirst potentiometer module to connect said modules to the face plate,and wherein said aligned openings are substantially parallel to the axisof rotation of said rotor.

12. The control as recited in claim 10, wherein the potentiometer modulerotor includes a movable contact connected to a sleeve and thepotentiometer module includes a collector disposed around said sleeveand axially to one side of said movable contact and in electricalcontact therewith, and a resistance track disposed around said sleeveand axially to the other side of said movable contact and in electricalcontact therewith.

13. The control as recited in claim 10, wherein said gear train includesa first sun gear connected to said outer shaft, a first planet gear setconnected to revolve around said first sun gear when the outer shaft isrotated to rotate said gear train output.

14. The control as recited in claim 13, wherein a second sun gear isconnected for rotation by said first planet gears, and a second set ofplanet gears connect to revolve around said second sun gear when it isrotated to rotate said gear train output.

15. The control as recited in claim 14, wherein there is a centralopening through said first and second sun gears through which said innershaft passes.

16. In a variable resistance module the combination comprising:

a housing having front and back walls with a compartment therebetweenand also having central openings in the walls communicating with thecompartment;

an electrical resistance track on the inside of one of said walls facinginto the compartment;

an electrical collector on the inside of the other of said walls andalso facing into the compartment, whereby said resistance track andcollector are spaced from one another in facing relation;

a rotor within said compartment journaled in said central openings forturning motion; and

contact means in said compartment mounted by said rotor for rotationtherewith that has a first sliding contact in engagement with saidresistance track and a second sliding contact in engagement with saidelectrical collector.

17. A variable resistance module as in claim 16 in which said resistancetrack and electrical collector are circular and located concentric withthe axis of rotation of said rotor; and

wherein said sliding contacts are spring biased in opposite axialdirections.

18. A variable resistance module as in claim 17 wherein said slidingcontacts are circumferentially aligned to minimize transverse torque onthe rotor.

19. A variable resistance module as in claim 16 having in combinationtherewith a bushing at the front of the module;

a rotatable control shaft in said bushing; and

a detachable coupling connection between the rear end of said shaft andsaid rotor.

20. The structure of claim 19 in combination with a second module likethe first module, said second module being attached to the rear of thefirst module, and there being a detachable coupling connection betweenthe rotors of the modules.

21. The structure of claim 19 in combination with a second module likethe first module, said second module being attached to the rear of thefirst module, the rotors and control shaft are hollow, a second innershaft extends through said hollow rotors and control shaft, and therebeing a coupling connection between the rotor of said second module andsaid second inner shaft.

22. A control formed by connecting together a plurality of physicallyidentical potentiometer modules, each module including:

a case having a front and a back wall spaced to define a compartmentbetween the walls;

a collector connected to said case and located within said compartment;

a resistance track connected to said case and located within saidcompartment; and

a rotor rotatably attached to said case and communicating throughopenings in the front and back walls thereof to couple with the rotorsof adjacent potentiometer modules.

23. The control as recited in claim 22, wherein an opening is formedthrough each rotor, and the rotors of adjacent modules are coupled bymeans of a link which has an opening that aligns with the openings inthe coupled rotors.

24. The control as recited in claim 22 in which a face plate is attachedto the front wall of one potentiometer module and a shaft journaled in abushing formed on said face plate couples with the rotor of said onepotentiometer module.

1. A potentiometer module the combination comprising: a case having afront and back surface; a rotor connected to said case to rotate aboutan axis, said rotor having a movable contact; a collector connected tosaid case and disposed axially to one side of said movable contact andin electrical contact therewith; and a resistance track connected tosaid case and disposed axially to the other side of said movable contactand in electrical contact therewith; wherein said rotor includes asleeve having ends which communicate with the front and back surfaces ofsaid case and said collector and resistance track are disposed aroundsaid sleeve.
 2. A potentiometer module as recited in claim 1, whereinsaid sleeve has identical coupling means at its ends.
 3. Thepotentiometer module as recited in claim 1, wherein said movable contactcomprises: a wiper which is spring biased against said resistance trackby a force acting axially in one direction; and a contact ring which isspring biased against said collector by a force acting axially in theopposite direction.
 4. The potentiometer module as recited in claim 1,wherein said resistance track is formed on an annular-shaped basedisposed around said rotor sleeve and connected to said case.
 5. Acontrol the combination comprising: a bushing adapted to attach to acontrol panel; a shaft extending through said bushing; a couplerconnected to the back end of said shaft; a first potentiometer modulehaving front and back surfaces, said first module including a rotorwhich communicates with the front surface of said first module toconnect with said coupler and which extends through said first module tocommunicate with its back surface; a second potentiometer module havingfront and back surfaces, said second module including a rotor whichcommunicates with the front surface of said second module to connectwith the rotor of said first module and which extends through saidsecond module to communicate with its back surface; and a plurality ofstack bolts each passing completely through said first and secondmodules to fasten them to the bushing.
 6. A control as recited in claim5, wherein said first and second potentiometer modules are structurallyidentical, each rotor having a sleeve which communicates with the frontand back surfaces of the module and a movable contact, each module alsohaving a collector disposed around said rotor sleeve and axially to oneside of said movable contact to make electrical contact therewith and aresistance track disposed around said rotor sleeve and axially to theother side of said movable contact to make electrical contact therewith.7. A control the combination comprising: a bushing adapted to attach toa control panel and having a shaft opening extending through it fromfront to back; a face plate disposed around the opening at the back endof the bushing and perpendicular to the central axis of the shaftopening; a first potentiometer module fastened to the face plate, saidfirst module having a rotor in alignment with the shaft opening axis,which rotor extends completely through the first module and has acentral concentric opening completely through it; an outer shaftrotatably retained within said shaft opening and connected to the rotorof said first module, said shaft having a central concentric opening; asecond potentiometer module structurally identical to the firstpotentiometer module and connected to the first potentiometer module,said second module having a rotor aligned with the rotor of said firstpotentiometer module; and an inner shaft rotatably retained within andpassing through the openings in the outer shaft and the rotor of thefirst module to connect with the rotor of the second module.
 8. Thecontrol as recited in claim 7 wHerein a plurality of stack bolts extendthrough aligned openings in the first and second potentiometer modulesto connect said modules to the face plate, wherein said aligned openingsare substantially parallel to the axis of rotation of said rotors. 9.The control as recited in claim 8 wherein the module rotors each includea movable contact connected to a sleeve and each module includes acollector disposed around said sleeve and axially to one side of saidmovable contact and a resistance track disposed around said sleeve andaxially to the other side of said movable contact.
 10. A control thecombination comprising: a bushing adapted to attach to a control panelor the like and having a shaft opening extending through it from frontto back; a face plate disposed around the opening at the back end of thebushing and perpendicular to the central axis of the shaft opening; agear reduction module fastened to the face plate, said gear reductionmodule including a gear train with an output which rotates at a reducedrate of rotation with respect to a rotatable input; an outer shaftrotatably retained within said shaft opening and connected to rotatesaid gear train input, said outer shaft having a central concentricopening; a first potentiometer module fastened to said gear reductionmodule, said first module having a rotor in alignment with the shaftopening axis and coupled to said gear train output, which rotor extendscompletely through the first potentiometer module and has a centralconcentric opening completely through it; and an inner shaft rotatablyretained within and passing through the outer shaft and reduction gearmodule to connect with the rotor of the first potentiometer module. 11.The control as recited in claim 10, wherein a plurality of stack boltsextend through aligned openings in the gear reduction module and firstpotentiometer module to connect said modules to the face plate, andwherein said aligned openings are substantially parallel to the axis ofrotation of said rotor.
 12. The control as recited in claim 10, whereinthe potentiometer module rotor includes a movable contact connected to asleeve and the potentiometer module includes a collector disposed aroundsaid sleeve and axially to one side of said movable contact and inelectrical contact therewith, and a resistance track disposed aroundsaid sleeve and axially to the other side of said movable contact and inelectrical contact therewith.
 13. The control as recited in claim 10,wherein said gear train includes a first sun gear connected to saidouter shaft, a first planet gear set connected to revolve around saidfirst sun gear when the outer shaft is rotated to rotate said gear trainoutput.
 14. The control as recited in claim 13, wherein a second sungear is connected for rotation by said first planet gears, and a secondset of planet gears connect to revolve around said second sun gear whenit is rotated to rotate said gear train output.
 15. The control asrecited in claim 14, wherein there is a central opening through saidfirst and second sun gears through which said inner shaft passes.
 16. Ina variable resistance module the combination comprising: a housinghaving front and back walls with a compartment therebetween and alsohaving central openings in the walls communicating with the compartment;an electrical resistance track on the inside of one of said walls facinginto the compartment; an electrical collector on the inside of the otherof said walls and also facing into the compartment, whereby saidresistance track and collector are spaced from one another in facingrelation; a rotor within said compartment journaled in said centralopenings for turning motion; and contact means in said compartmentmounted by said rotor for rotation therewith that has a first slidingcontact in engagement with said resistance track and a second slidingcontact in engagement with said electrical collector.
 17. A vaRiableresistance module as in claim 16 in which said resistance track andelectrical collector are circular and located concentric with the axisof rotation of said rotor; and wherein said sliding contacts are springbiased in opposite axial directions.
 18. A variable resistance module asin claim 17 wherein said sliding contacts are circumferentially alignedto minimize transverse torque on the rotor.
 19. A variable resistancemodule as in claim 16 having in combination therewith a bushing at thefront of the module; a rotatable control shaft in said bushing; and adetachable coupling connection between the rear end of said shaft andsaid rotor.
 20. The structure of claim 19 in combination with a secondmodule like the first module, said second module being attached to therear of the first module, and there being a detachable couplingconnection between the rotors of the modules.
 21. The structure of claim19 in combination with a second module like the first module, saidsecond module being attached to the rear of the first module, the rotorsand control shaft are hollow, a second inner shaft extends through saidhollow rotors and control shaft, and there being a coupling connectionbetween the rotor of said second module and said second inner shaft. 22.A control formed by connecting together a plurality of physicallyidentical potentiometer modules, each module including: a case having afront and a back wall spaced to define a compartment between the walls;a collector connected to said case and located within said compartment;a resistance track connected to said case and located within saidcompartment; and a rotor rotatably attached to said case andcommunicating through openings in the front and back walls thereof tocouple with the rotors of adjacent potentiometer modules.
 23. Thecontrol as recited in claim 22, wherein an opening is formed througheach rotor, and the rotors of adjacent modules are coupled by means of alink which has an opening that aligns with the openings in the coupledrotors.
 24. The control as recited in claim 22 in which a face plate isattached to the front wall of one potentiometer module and a shaftjournaled in a bushing formed on said face plate couples with the rotorof said one potentiometer module.